The aim of the proposed research is to characterize the energetics of fragmentation of large multiprotein complexes. Several model systems, including the complexes of small heat shock protein, chaperonin GroEL, and transthyretin, will be studied. The excitation and subsequent dissociation of these systems will be achieved in a modified quadrupole time-of-flight (Q-TOF) mass spectrometer. This instrument allows ion activation by either surface induced dissociation (SID) or collision induced dissociation (CID) and will enable the comparison of these different techniques. The efficient transfer of kinetic to vibrational energy that is achieved via SID will allow the study of multiprotein complexes over a wide range of internal energies. Several factors that likely govern the dissociation of these complexes will be investigated, including activation energy, number and size of subunits in a complex (vibrational degrees of freedom), their interfacial surface area, and types of binding interactions (hydrophobic v. polar). In a broad sense, these studies are aimed to facilitate the development of mass spectrometric strategies for the structural characterization and eventual assignment of biological funtion of multiprotein complexes.